1. Field of the Invention
This invention relates to a method for the production of a polymer. More particularly, this invention relates to a method for the production of a polymer from an aqueous solution of a corresponding .alpha., .beta.-ethylenically unsaturated monomer.
2. Description of Prior Art
Heretofore, polymers obtained by polymerizing aqueous solutions of such .alpha., .beta.-ethlenically unsaturated monomers as acrylic acid salts, methacrylic acid salts, and acrylamides have found extensive utility as thickener, flocculants, dispersants, water absorbents, etc.
The aqueous solution of an .alpha., .beta.-ethylenically unsaturated monomer is inhibited from being smoothly polymerized by dissolved oxygen. When the solution is prepared for polymerization, therefore, it is necessary that the dissolved oxygen be removed from the solution in advance of the polymerization. The idea of effecting the removal of dissolved oxygen in each polymerization vessel or in each cycle of polymerization cannot be called very wise from the technological point of view. Where the polymerization involves use of a plurality of polymerization vessels or where it is carried out in the form of a continuous operation, the practice of effecting the removal of dissolved oxygen collectively on the aqueous monomer solution compounded at once in a large volume and subjecting the aqueous monomer solution now free from the dissolved oxygen to polymerization proves more rational. Unfortunately, the aqueous monomer solution so deprived of dissolved oxygen is liable to be polymerized by light or impurities. Particularly when the aqueous monomer solution is prepared in a highly concentrated form or when the aqueous monomer solution happens to contain a cross-linking monomer, once polymerization starts on the aqueous monomer solution, the system loses fluidity so much as to render desired removal of heat of polymerization difficult. Thus, there is a possibility that the aqueous monomer solution will suddenly undergo polymerization in the container used for holding the solution or in the pipe used for transferring the solution from the container to the polymerization vessel. In this respect, the aqueous monomer solution compounded at once in a large volume and gradually putting the aqueous monomer solution freed from the dissolved oxygen to polymerization does not prove desirable. If the polymerization does not suddenly occur, it has a possibility of entailing occurrence of an insoluble gel. This gel, when left to take its own course, may gradually grow and eventually clog the pipe leading into the polymerization vessel and jeopardize the plant's operation. When the polymerization is carried out batchwise in a plurality of polymerization vessels or when it is carried out continuously in one polymerization vessel, the practice of effecting the removal of dissolved oxygen continuously and quickly and allowing the aqueous monomer solution freed from the dissolved oxygen to be fed continuously to the polymerization vessel proves particularly desirable. The desirability of perfecting a method capable of continuously removing dissolved oxygen from the aqueous monomer solution has come to find growing recognition.
As one approach to the solution, there has been proposed a method which effects instantaneous deoxidation of an aqueous monomer solution while the aqueous monomer solution is being transferred through a pipe to a polymerization vessel by forwarding an inert gas into contact with the aqueous monomer solution through a diffusing tube or a diffusing panel provided with fine perforations therein (Japanese Patent Publication No. SHO 54(1979)-37,910). In the operation of this method, after protracted use of the diffusing tube or diffusing panel, the insoluble polymer gradually adheres thereto and eventually clogs the fine perforations formed therein and, as the result, the flow of the inert gas encounters growing resistance and the supply of the inert gas no longer proceeds smoothly. If the gel deposit is left growing, it will come off the diffusing tube or diffusing panel and clog the pipe, or even give adverse effects on the quality of the produced polymer. Thus, the apparatus used for working the method can hardly endure protracted use.
An object of this invention, therefore, is to provide a novel method for the production of a polymer.
Another object of this invention is to provide a method for attaining stable production of a polymer from an aqueous solution of a corresponding monomer by very rapidly and continuously removing dissolved oxygen from the aqueous monomer solution and enabling the aqueous monomer solution freed from the dissolved oxygen to be uniformly supplied to the site of polymerization in spite of protracted use of an apparatus used for working the method.